What I ussually do is know where my nocking point is. From there I usually tie about 2 - 2 1/2 inches above and below that point. Total serving is about 4-5 inches. That's all you really need.
I started typing out a description on how to do it and was confusing myself
Didn't even think to try to write it out. Perfect example of a picture worth a thousand words.
You may also want to put just a drop of glue at the cut off thread. Not a lot though, you don't want it to seep through the serving, and get onto the string.